Periodicity: OxfordAQA International IAL Chemistry

Flashcards covering the classification of elements and the physical property trends (atomic radius, ionisation energy, and melting points) of Period 3 elements.

Periodic Table

A list of all known elements arranged in order of increasing atomic number (proton number).

Periods

Horizontal rows in the Periodic Table where all atoms have the same number of shells.

Groups

Vertical columns in the Periodic Table where atoms have similar electronic configurations in the outer shell and show similar chemical properties.

Periodicity

The study of periodic trends where the properties of elements repeat themselves in each period as atomic number increases.

Structure-based Classification (Blocks)

The division of elements into s-block, p-block, d-block, and f-block based on which sub-shell their outer electron is found in.

Atomic Radius

The distance between the nucleus and the outermost electron of an atom, measured by halving the distance between the nuclei of two atoms of the same element.

Period 3 Atomic Radius Trend

The atomic radius decreases across Period 3 (from $0.157\,nm$ for $Na$ to $0.099\,nm$ for $Cl$) because increasing nuclear charge pulls the electrons in the same shell closer to the nucleus while shielding remains constant.

First Ionisation Energy

The energy required to remove one mole of electrons from one mole of atoms of an element to form one mole of $1+$ ions, expressed as $X(g) \rightarrow X^+(g) + e^-$.

First Ionisation Energy of Sodium

The energy characteristic of removing sodium's outer electron, valued at $IE = +496\,kJ\,mol^{-1}$.

Ionisation Energy Trend Exceptions (Period 3)

Two elements deviate from the general increase across the period: Aluminium has a lower first ionisation energy than Magnesium, and Sulfur has a lower first ionisation energy than Phosphorus.

Metallic Bonding (Na, Mg, Al)

Strong electrostatic forces of attraction between positive metal ions and a 'sea' of delocalised electrons donated from their outer shells ($Na$ donates 1, $Mg$ donates 2, and $Al$ donates 3).

Silicon (Melting Point)

The element with the highest melting point ($1683\,K$) in Period 3 due to its giant molecular structure where each atom is held by four strong covalent bonds.

Van der Waals' forces

Weak intermolecular forces between simple molecules ($P_4$, $S_8$, $Cl_2$, and $Ar$) that require little energy to overcome, resulting in lower melting points compared to metals and giant molecular structures.

Melting Point Hierarchy (P-Ar)

The order of melting points for the non-metallic elements from highest to lowest is $S_8 > P_4 > Cl_2 > Ar$, based on the size of the molecules and the number of electrons affecting van der Waals' forces.